The decline of auditory discrimination abilities is a common and troublesome companion of aging that interferes with the perception of speech and other important sounds. This problem that interferes with the perception of speech and other important sounds. This problem is often associated with age-related loss of hearing sensitivity (presbycusis), but can also occur in the absence of significant threshold elevations. In either case, a breakdown of normal neural coding processes in the auditory central nervous system must plan an important part in the loss of discrimination ability. The proposed research project will investigate this problem by studying neural coding using two inbred mouse strains as models: the C57BL/6J strain, which shows substantial presbycusic loss, and the CBA/J strain, which shows little sensitivity loss with age. Neurophysiological experiments will be performed in mice in several age-ranges, obtaining extracellular neuronal recodings from the anteroventral cochlear nucleus and central nucleus of the inferior colliculus. Age-related changes in neuronal response parameters thought to be involved in the coding of frequency, intensity, and repetition eate of sounds will be described in detail. New information will thus be obtained on how neurophysiological processes change as a function of age and on their relationship to presbycusic loss of sensitivity and to aging per se (by using two strains). This will provide a crucial step toward understanding the problem of age-related loss of auditory discrimination abilities.